Explosives and other controlled substances, such as drugs, have become major societal problems. Increasingly, terrorist acts using explosives are becoming a problem not only for countries in the Middle East but also for Western countries in other parts of the world. Explosives constitute a weapon used by terrorists and insurgents, wherein the explosives may be hidden in a myriad of devices; however, it is typically difficult for a person handling explosives to avoid contamination after coming into contact with an explosive or explosive device because explosives readily adhere to surfaces.
In addition to explosives, drug abuse has been a longstanding problem for Western countries and consumes large amounts of law enforcement resources each year. Canines, metal detectors, and “sniffer” detectors have been used at various locations, such as airports, border crossings, and the like to detect explosive devices and illegal drugs. These measures have had mixed success.
Another measure that has been employed to detect contraband substances has been to collect loose particles from surfaces or skin with a vacuum cleaner or a swipe. The swipe or the particles collected by the vacuum are then heated to release the vaporizable material for analysis. This approach is in routine use at airports throughout the world for screening airline passengers. An example of such a system is the Barringer™ Ion Scan System™; however, this technique has drawbacks. For example, the use of swipes or particle vacuums is an intermittent process, which requires manual intervention between the sampling and analysis. This is a time consuming approach that is inherently slow, although it may optionally be used in conjunction with at least one embodiment of the present invention.
Previously disclosed devices for volatilizing certain substances for detection include a high-energy apparatus disclosed in U.S. Pat. No. 6,895,804. The content of U.S. Pat. No. 6,895,804 is incorporated herein by reference in its entirety. The landmine detection apparatus of the '804 patent applies a relatively high amount of energy to the sample target that is generally intended to be soil. To provide the requisite energy, the radiation source of the '804 patent is powered by a relatively high amount of energy, and therefore, is limiting in its ability to serve as a self-contained backpack unit, handheld device, or other relatively compact portable device. In addition, high-energy strobes are slow to recharge, utilize kilowatts of energy to power, and are heavy as a self-contained unit that includes a power source.
U.S. Pat. No. 6,828,795, incorporated herein by reference, suggests use of an ion mobility spectrometer with a heat source, but energy levels have not been provided. U.S. Patent Application Publication No. 2005/0007119 A1, related to the '795 patent, is also incorporated herein by reference. The '795 patent discloses using an electrostatic precipitator to take out particulates, presumably to keep them out of the ion mobility spectrometer. It is noted here that, in at least one embodiment, the present invention advantageously releases a plume of particulates that is then able to form at least part of the signal.
Typical trace explosive detectors employing vapor and/or particle analyses rely on an interval-based analysis that requires discrete and separate steps for (1) sampling and (2) detection. The combination of these two steps may take anywhere from 15 to 60 seconds, or more. Thus, it would be advantageous to provide an apparatus for sampling multiple target surfaces while the detector is processing the sampled information.
Surface Enhanced Raman Spectroscopy (SERS) can be used for trace detection of chemical contaminants, such as explosives or drugs. SERS employs microscopically roughened, or “activated” metals, normally noble metals, that adsorb the compound of interest. Existing SERS detectors have traditionally been hindered in application due to the length of time that the SERS substrate surface remained available for new sample material to adsorb to the nano-texture of the substrate. Therefore, the SERS substrate requires cleaning or refreshing to continue to function properly. Such cleaning of the substrate surface has been accomplished in prior art by a number of methods.
One such method includes disposing of the used substrate and using a new substrate. As a result, this further requires the effort of recalibration of the signal amplification factor, or otherwise having to fabricate the substrate surface using extreme precision controls so that recalibration is not necessary. Either way, the result is high costs because of instrument down-time for substrate replacement and costs associated with fabrication and procurement of the replacement substrates.
Another way of refreshing the SERS substrate is to heat the substrate to desorb the adsorbed materials. This is slow and requires considerable power to heat and subsequently re-cool the substrate, thus making it unattractive for battery powered equipment.
A further method of cleaning or refreshing the SERS substrate is to increase the ambient air flow across the substrate surface to favor desorption of the adsorbed materials from the substrate due to solid-gas partitioning. However, this process will only restore the surface over time if the air flowing across the surface is clean and does not contain other materials that will in-turn adsorb on the surface. In addition, this method relies on rather slow thermodynamics and the time it takes will cost the system overall power in idle time. In general, this process is slow because the desorption of contaminants with low vapor pressures is particularly time consuming.
Yet another method of cleaning or refreshing the SERS substrate is to remove the substrate and clean the substrate using solvent rinsing, heating, and/or wiping with a clean or solvent soaked swab. Although relatively quick, this costs labor, is prone to human neglect and/or error, and is subject to irreproducibility. Furthermore, contaminates from the cleaning process may also adsorb onto the substrate. Thus, it would be advantageous to provide an improved means for refreshing or cleaning the SERS substrate.
As noted above, present techniques for airport security include sometimes screening baggage for trace explosives by manually swiping the surface of the baggage and analyzing the swipe, such as by using Ion Mobility Spectrometry. Not all bags are tested for trace explosives, with carry-on baggage typically being X-rayed but not always screened for traces of explosives. Thus, there would be an advantage to automatically screening all baggage, whether checked or carry-on, for explosives. In addition, upon arrival at a destination airport, government agencies at the destination airport typically also screen baggage, wherein such screen efforts typically include searches for drugs. Thus, it would be advantageous to be able to automatically screen baggage upon arrival, such as when baggage is unloaded from international flights. Accordingly, among other types of screening uses, such as crime scene analysis, there is clearly a need for automatically screening airline baggage and carry-on items for traces of explosives and drugs.